Abstract 2385: Discovery of highly specific claudin 6 monoclonal antibodies

Abstract

Claudin 6 (CLDN6) is an oncofetal tight junction protein involved in the cell-to-cell adhesion of epithelial and endothelial cell sheets. Although silenced in healthy adult human tissues, CLDN6 expression has been found in ovarian, gastric, pediatric, and other cancer tissues and can lead to a poor prognosis. Monoclonal antibody (MAb) discovery against CLDN6 has been encumbered by the high homology of endogenously expressed claudin 9 (CLDN9), which varies from CLDN6 by only 3 amino acids in the extracellular domain. Our MPS Antibody Discovery platform utilizes proprietary technologies to overcome key barriers to MAb discovery, enabling the isolation of MAbs against multipass membrane proteins such as CLDN6. Using the MPS platform, we have successfully isolated and characterized panels of highly specific MAbs to CLDN6. Nine chickens were immunized with the target antigen, and titer was achieved in all but one animal. Following 2 rounds of phage panning, we screened 2,000 clones for CLDN6 specificity, identifying 788 hits and 68 unique VH CDR3 families. From these clones, 72 antibodies were selected for binding to CLDN6 and CLDN6/9. Two lead antibodies, IM-171 and IM-136, showed high specificity and high affinity to CLDN6 but not to claudins 3, 4, or 9. Using high-resolution Shotgun Mutagenesis Epitope Mapping, we confirmed that our lead candidate MAbs bind distinct residues on CLDN6 compared to previously described MAbs. Specificity analysis with our Membrane Proteome Array revealed no significant binding of either of our lead MAbs to any other membrane protein in the human proteome, including any of the other 20+ claudin proteins. Both of our lead MAbs bound endogenously expressed CLDN6 on ovarian carcinoma (PA-1) cells. Our preclinical CLDN6 antibodies are now being developed for use in various formats, including bispecifics, antibody-drug conjugates, and CAR-T applications. Citation Format: L Joe Stafford. Discovery of highly specific claudin 6 monoclonal antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2385.